12: RIP Routing Protocol

RIP (Routing Information Protocol) is a distance vector routing protocol.

In this protocol, the metric used to calculate the path cost is the ‘hop count’.

The maximum hop count in the RIP protocol is ‘15’. It means that, a network that uses the RIP routing protocol cannot contain more than 15 routers, which is a disadvantage in the RIP protocol.

RIP timers

Route update timer: it is the interval between the routing updates (30 sec.).

Route invalid timer: it is the period before a router determines that a route is unreachable (180 sec.).

Route flush timer: it is the period between the route ‘invalid’ state, and its removal from the routing table (240 sec.).

Holddown timer: the router will be in the hold down state during this period, this is done after an update packet is received telling that a certain route is unreachable (default = 180 sec.).

RIP configuration

Image2142.JPG

To configure a router to use the RIP routing protocol, we write the following commands,

Router(config)# router rip

Router(config-router)# network ip address

To verify the router’s RIP configuration, we need to see the routing table of the router.

To see the routing table, we write the following command,

Router# show ip route

12.1 RIP is a classful routing protocol

A ‘classful routing protocol’ means that the RIP protocol does not send the subnet mask information with the network updates.

Therefore, RIP does not support the ‘discontiguous networks’, the ‘CIDR’, and the ‘VLSM’. This will be discussed in the following pages.

12.1.1 Discontiguous networks

In dicontiguous networks, every router thinks it has the only 10.0.0.0/8 network

5721.jpgFigure 12.1: the discontiguous networks

12.1.2 CIDR

CIDR (Classless Inter-Domain Routing) is to route the data between the networks that has subnet mask information are different from the default subnet masks.

Image2150.JPGFigure 12.2: CIDR

12.1.3 VLSM

VLSM (Variable Length Subnet Mask) is to have networks with variable subnet masks that are subnetted from one network IP.

5732.jpg

5741.jpgFigure 12.2: VLSM

12.2 RIPv2 (RIP version 2)

The advantage of the RIPv2 protocol over the RIP protocol is that, it is a ‘classless routing protocol’

This means that RIPv2 sends the subnet mask information with the network updates.

Therefore, RIPv2 supports the ‘dicontguous networks’, the ‘CIDR’ and the ‘VLSM’.

12.2.1 RIPv2 configuration

In order to configure the router to work with RIPv2, we write the following commands,

Router(config)# router rip

Router(config-router)# version 2

Router(config-router)# network ip address

Router(config-router)# no auto-summary

12.2.2 Passive Interface configuration

We can configure any interface as a ‘passive interface’, this is used in order to not send or receive any network updates on a certain interface.

To configure the ‘passive interface, we use the following command,

Router(config-router)# passive-interface interface

12.3 IGRP routing protocol

IGRP (Interior Gateway Routing Protocol) is a Cisco proprietary protocol, which means that it could not be configured on any device except a Cisco device.

It is a classful routing protocol.

The maximum hop count is ‘255’, which is an advantage over the RIP protocol, which has only ‘15’.

The metric used to calculate the path cost is the ‘Delay’ and the ‘bandwidth’.

Currently, Cisco does not support the IGRP protocol.